242 [Dee. 15, 
Cope. ] 
saurus, an important series of changes of shape (but not in complexity) 
appears, which may be represented thus :—Fig. 5; the first being hu- 
merus, second ulna, third and fourth carpals (tarsals) the last phalanges, 
which are first specialized in this genus. 
By far the most usual modification is however complication by dupli- 
cated and triplicated and still more highly multiplied repetition in some t 
segments of the archetype, and its omission in other segments. Thus in F 
in the Tenia, the cephalic segments are much modified, and the nature 
of its repetitions might be thus expressed :—-Fig. 6 ; the simpler segments 
representing the body segment, the two complex, representing these of 
the head. In each, it will be observed, the complication is represented 
by loops of similar form, and each loop of dots which represent the cells 
in the first linear (fig. 1) arrangement. 
A somewhat similar figure might represent the nature of the complica- 
tion in the Myriapod. In the insect the additional complications of the 
thoracic segments would alter the diagram near the middle. 
In the vertebrate cranium, a somewhat similar diagram might be used, 
except that the modification of the segments or vertebra, as compared with 
the segments of the vertebral column, is not by repetition with modifica- 
tion of the parts of each segment, but rather by modification of the 
forms of the parts of the segments. The basi-cranial segments thus com- 
pare with the dorsal vertebrae as the segments of the limb of Plestosaurus 
do to those of Ichthyosaurus. 
The above considerations have reference to repetition of parts in a 
linear direction. Centrifugal repetition is seen in the addition of cham- 
bers to the heart, by the subdivision in the earliest stages into auricle and 
ventricle in the linear direction, considered in connection with the earlier 
division of each in the transverse direction, by the growth of partitions. 
This mode of repetitive addition is not readily represented by diagram. 
A good example of repetitive addition in both linear and transverse 
direction, may be found in the successive complication of tooth structure 
seen in mammalia. In the dolphin, the dental series may be repre- 
sented thus:—Fig. 7; in the squalodon thus:—Fig. 8; in the cat:—Fig. 9; 
in the dog:—Fig. 10; in man :—Fig. 11; in some insectivora :—Fig. 12. 
The circles represented here, are each a simple cusp. 
In conclusion, the directions of Repetitive growth may be tabulated as 
follows: The types to the left represent the original ; to the right, the 
derivative. 
( More bilaterally 
| symmetrical. 
Longitudin’] antero-pos- \ 
terior and bilateral. — | 
| More antero-pos- | Only antero- 
L teriorly. \ posterior. 
( In plane. 
| 
4 Only bilateral. 
( 
| 
Centrifugal. { 
| 
U 
Centrifugal. 
| In globe. 
